1. Field of the Invention
The present invention relates to torque controllers and torque limiters and, more particularly, to fully adjustable torque controllers and limiters for rotationally driven systems.
2. Prior Art
In order to protect rotating mechanical systems from damage caused by loads that exceed the limit for which the system was designed, a series of devices called torque limiters have been employed. They are also sometimes called torque limiting clutches. Torque limiters are generally energy or load dumping devices which interface between motive parts of a system and act to prevent damage to the motive parts under excessive loading conditions which are inadvertently imposed on the motive parts. The use of torque limiters in motive systems is highly desirable in order to accurately limit the maximum loading condition to which a system will be subjected, and hence, do away with any reasonable possibility that the system will be subjected to undesired loads. Providing an accurate limit to the maximum loading condition on a system facilitates a reduction in the size, weight, and complexity of the motive parts of the system with an associated reduction in the cost of the parts. Nevertheless, torque limiters of the prior art used on rotating or shaft driven systems have been large, heavy, bulky, complex, and expensive devices, rendering them unsatisfactory for most applications. The prior art torque limiters tend to be of two types. One type of torque limiter of the prior art operates based on friction, generally using either slip clutches and/or visco-elastic materials to absorb excess energy. This friction type of torque limiter in effect converts the excess load into thermal energy (i.e. heat). The heat generated by the torque limiter subjects the torque limiter and adjoining parts to high temperatures, unless the heat generated by the torque limiter is transferred by suitable means away from the torque limiter. Thus, friction type torque limiters of the prior art must employ materials suitable for use at high temperatures, and must be provided with heat dissipation means resulting in increased size, weight, complexity, and cost of this type of torque limiters. Although slip repeat capability has a broad tolerance (≈xc2x110%), friction clutches do reengage automatically when the overload subsides without the need to shut down, thereby avoiding costly downtime. Periodic adjustment and friction lining replacement is required depending upon torque, frequency and duration of activation, and rotational speed of operation. These conventional devices do not function well under adverse ambient conditions because of changes in the coefficient of friction.
Another type of torque limiter of the prior art used on rotating drive systems generally relies on spring loaded rollers or balls which engage complementing pockets or detents to transfer torque between outer and inner rings of the torque limiter. When the torque across the torque limiter exceeds a predetermined amount the spring loaded balls are disengaged from the pockets allowing the outer and inner rings to slip relative to each other. This type has less friction, lasts longer, and repeats more accurately (xc2x13 to 5%) than the friction type. They can also reset to a precise orientation. Spring loaded ball torque limiters are however large, heavy and costly arising from the large number of parts used to hold and support many individual balls and springs in the torque limiter. Each application appears unique and involves a large number of independent design variables. There is no industry standard. Many manufacturers produce ball type torque limiters, serving a limited market, with a diversity of design and custom machined parts, all of which means low volume and high cost. These limiters are not modularized, adding to the diversity of models and further cutting the size of production runs. The torque limiter of the present invention overcomes the problems of the prior art.
In accordance with a first embodiment of the present invention, a torque coupler for coupling rotatable inner and outer parts is provided. The torque coupler comprises an inner slip section, and an outer slip section. The inner slip section is connected to the inner rotatable part to rotate with the inner part when the inner part is rotating. The inner slip section has an outer circumferential surface disposed around the inner part. The outer circumferential surface has a predetermined number of detents formed therein. The outer slip section is connected to the outer rotatable part to rotate with the outer part when the outer part is rotating. The outer slip section is seated against the inner slip section with an inner surface of the outer slip section in contact with the outer surface of the inner slip section. The inner surface of the outer slip section has a predetermined number of spring loaded teeth which are biased for engaging the detents in the outer surface of the inner slip section. This engagement locks the inner slip section and the outer slip section and transfers an applied torque between the inner and outer mating parts.
In accordance with a second embodiment of the present invention, a torque limiter coupling for coupling rotatable radially spaced first and second parts is provided. The torque limiter coupling comprises a first slip ring and a second slip ring. The first slip ring is sized and shaped to be fixedly mounted onto the first rotatable part. The first slip ring has a circumferential slip surface disposed radially between the first and second parts when the slip ring is mounted onto the first part. The slip surface has a number of detents formed therein. The second slip ring is sized and shaped to be fixedly mounted onto the second rotatable part. The second slip ring has a predetermined number of resilient spring fingers extending radially between the first and second parts when the second slip ring is mounted onto the second part. Each of the resilient spring fingers has a tooth at a tip of the spring finger for engaging a corresponding one of the detents on the first slip ring. This engagement transfers torque between the first slip ring and the second slip ring.
In accordance with a third embodiment of the present invention, an adjustable torque limiting coupling for coupling rotatable radially spaced first and second parts is provided. The torque limiting coupling comprises a housing, a slip ring, a slip assembly, and a spring preload adjustment mechanism. The housing is adapted to be fixedly mounted to the first rotatable part to rotate with the first part. The slip ring is disposed in the housing. The slip ring has a bore therein for mating the slip ring to the second rotatable part to rotate with the second rotatable part. The slip ring has a circumferential slip surface radially spaced relative to the second part when the slip ring is mated to the second part. The slip surface has a number of detents formed therein. The slip assembly is connected to the housing to rotate with the housing. The slip assembly interfaces radially between the slip ring and the housing. The slip assembly comprises a slip pad, with a predetermined number of teeth, and a multiple spring member. The multiple spring member biases the slip pad against the circumferential slip surface of the slip ring, and engages the teeth of the slip pad to the detents on the slip ring. The spring preload adjustment mechanism is connected to the housing for adjusting the spring preload of the multiple spring member against the slip pad. The spring preload adjustment mechanism is adjustable when at least one of the first, or second rotatable parts is rotating.